Hack to allow concat to work even when an Array isn't assignable to ReadonlyArray

Author: Andy Hanson

src/lib/es5.d.ts

@@ -992,12 +992,13 @@ interface ReadonlyArray<T> {
       * Combines two or more arrays.
       * @param items Additional items to add to the end of array1.
       */
-    concat(...items: ReadonlyArray<T>[]): T[];
+    // TODO: https://github.com/Microsoft/TypeScript/issues/20454
+    concat(...items: (T[] | ReadonlyArray<T>)[]): T[];
     /**
       * Combines two or more arrays.
       * @param items Additional items to add to the end of array1.
       */
-    concat(...items: (T | ReadonlyArray<T>)[]): T[];
+    concat(...items: (T | T[] | ReadonlyArray<T>)[]): T[];
     /**
       * Adds all the elements of an array separated by the specified separator string.
       * @param separator A string used to separate one element of an array from the next in the resulting String. If omitted, the array elements are separated with a comma.
@@ -1113,12 +1114,12 @@ interface Array<T> {
       * Combines two or more arrays.
       * @param items Additional items to add to the end of array1.
       */
-    concat(...items: ReadonlyArray<T>[]): T[];
+    concat(...items: (T[] | ReadonlyArray<T>)[]): T[];
     /**
       * Combines two or more arrays.
       * @param items Additional items to add to the end of array1.
       */
-    concat(...items: (T | ReadonlyArray<T>)[]): T[];
+    concat(...items: (T | T[] | ReadonlyArray<T>)[]): T[];
     /**
       * Adds all the elements of an array separated by the specified separator string.
       * @param separator A string used to separate one element of an array from the next in the resulting String. If omitted, the array elements are separated with a comma.

tests/baselines/reference/arrayConcat2.types

@@ -5,17 +5,17 @@ var a: string[] = [];
 
 a.concat("hello", 'world');
 >a.concat("hello", 'world') : string[]
->a.concat : { (...items: ReadonlyArray<string>[]): string[]; (...items: (string | ReadonlyArray<string>)[]): string[]; }
+>a.concat : { (...items: (string[] | ReadonlyArray<string>)[]): string[]; (...items: (string | string[] | ReadonlyArray<string>)[]): string[]; }
 >a : string[]
->concat : { (...items: ReadonlyArray<string>[]): string[]; (...items: (string | ReadonlyArray<string>)[]): string[]; }
+>concat : { (...items: (string[] | ReadonlyArray<string>)[]): string[]; (...items: (string | string[] | ReadonlyArray<string>)[]): string[]; }
 >"hello" : "hello"
 >'world' : "world"
 
 a.concat('Hello');
 >a.concat('Hello') : string[]
->a.concat : { (...items: ReadonlyArray<string>[]): string[]; (...items: (string | ReadonlyArray<string>)[]): string[]; }
+>a.concat : { (...items: (string[] | ReadonlyArray<string>)[]): string[]; (...items: (string | string[] | ReadonlyArray<string>)[]): string[]; }
 >a : string[]
->concat : { (...items: ReadonlyArray<string>[]): string[]; (...items: (string | ReadonlyArray<string>)[]): string[]; }
+>concat : { (...items: (string[] | ReadonlyArray<string>)[]): string[]; (...items: (string | string[] | ReadonlyArray<string>)[]): string[]; }
 >'Hello' : "Hello"
 
 var b = new Array<string>();
@@ -25,8 +25,8 @@ var b = new Array<string>();
 
 b.concat('hello');
 >b.concat('hello') : string[]
->b.concat : { (...items: ReadonlyArray<string>[]): string[]; (...items: (string | ReadonlyArray<string>)[]): string[]; }
+>b.concat : { (...items: (string[] | ReadonlyArray<string>)[]): string[]; (...items: (string | string[] | ReadonlyArray<string>)[]): string[]; }
 >b : string[]
->concat : { (...items: ReadonlyArray<string>[]): string[]; (...items: (string | ReadonlyArray<string>)[]): string[]; }
+>concat : { (...items: (string[] | ReadonlyArray<string>)[]): string[]; (...items: (string | string[] | ReadonlyArray<string>)[]): string[]; }
 >'hello' : "hello"
 

tests/baselines/reference/arrayConcat3.js

@@ -0,0 +1,12 @@
+//// [arrayConcat3.ts]
+// TODO: remove lib hack when https://github.com/Microsoft/TypeScript/issues/20454 is fixed
+type Fn<T extends object> = <U extends T>(subj: U) => U
+function doStuff<T extends object, T1 extends T>(a: Array<Fn<T>>, b: Array<Fn<T1>>) {
+    b.concat(a);
+}
+
+
+//// [arrayConcat3.js]
+function doStuff(a, b) {
+    b.concat(a);
+}

tests/baselines/reference/arrayConcat3.symbols

@@ -0,0 +1,32 @@
+=== tests/cases/compiler/arrayConcat3.ts ===
+// TODO: remove lib hack when https://github.com/Microsoft/TypeScript/issues/20454 is fixed
+type Fn<T extends object> = <U extends T>(subj: U) => U
+>Fn : Symbol(Fn, Decl(arrayConcat3.ts, 0, 0))
+>T : Symbol(T, Decl(arrayConcat3.ts, 1, 8))
+>U : Symbol(U, Decl(arrayConcat3.ts, 1, 29))
+>T : Symbol(T, Decl(arrayConcat3.ts, 1, 8))
+>subj : Symbol(subj, Decl(arrayConcat3.ts, 1, 42))
+>U : Symbol(U, Decl(arrayConcat3.ts, 1, 29))
+>U : Symbol(U, Decl(arrayConcat3.ts, 1, 29))
+
+function doStuff<T extends object, T1 extends T>(a: Array<Fn<T>>, b: Array<Fn<T1>>) {
+>doStuff : Symbol(doStuff, Decl(arrayConcat3.ts, 1, 55))
+>T : Symbol(T, Decl(arrayConcat3.ts, 2, 17))
+>T1 : Symbol(T1, Decl(arrayConcat3.ts, 2, 34))
+>T : Symbol(T, Decl(arrayConcat3.ts, 2, 17))
+>a : Symbol(a, Decl(arrayConcat3.ts, 2, 49))
+>Array : Symbol(Array, Decl(lib.d.ts, --, --), Decl(lib.d.ts, --, --))
+>Fn : Symbol(Fn, Decl(arrayConcat3.ts, 0, 0))
+>T : Symbol(T, Decl(arrayConcat3.ts, 2, 17))
+>b : Symbol(b, Decl(arrayConcat3.ts, 2, 65))
+>Array : Symbol(Array, Decl(lib.d.ts, --, --), Decl(lib.d.ts, --, --))
+>Fn : Symbol(Fn, Decl(arrayConcat3.ts, 0, 0))
+>T1 : Symbol(T1, Decl(arrayConcat3.ts, 2, 34))
+
+    b.concat(a);
+>b.concat : Symbol(Array.concat, Decl(lib.d.ts, --, --), Decl(lib.d.ts, --, --))
+>b : Symbol(b, Decl(arrayConcat3.ts, 2, 65))
+>concat : Symbol(Array.concat, Decl(lib.d.ts, --, --), Decl(lib.d.ts, --, --))
+>a : Symbol(a, Decl(arrayConcat3.ts, 2, 49))
+}
+

tests/baselines/reference/arrayConcat3.types

@@ -0,0 +1,33 @@
+=== tests/cases/compiler/arrayConcat3.ts ===
+// TODO: remove lib hack when https://github.com/Microsoft/TypeScript/issues/20454 is fixed
+type Fn<T extends object> = <U extends T>(subj: U) => U
+>Fn : Fn<T>
+>T : T
+>U : U
+>T : T
+>subj : U
+>U : U
+>U : U
+
+function doStuff<T extends object, T1 extends T>(a: Array<Fn<T>>, b: Array<Fn<T1>>) {
+>doStuff : <T extends object, T1 extends T>(a: Fn<T>[], b: Fn<T1>[]) => void
+>T : T
+>T1 : T1
+>T : T
+>a : Fn<T>[]
+>Array : T[]
+>Fn : Fn<T>
+>T : T
+>b : Fn<T1>[]
+>Array : T[]
+>Fn : Fn<T>
+>T1 : T1
+
+    b.concat(a);
+>b.concat(a) : Fn<T1>[]
+>b.concat : { (...items: (Fn<T1>[] | ReadonlyArray<Fn<T1>>)[]): Fn<T1>[]; (...items: (Fn<T1> | Fn<T1>[] | ReadonlyArray<Fn<T1>>)[]): Fn<T1>[]; }
+>b : Fn<T1>[]
+>concat : { (...items: (Fn<T1>[] | ReadonlyArray<Fn<T1>>)[]): Fn<T1>[]; (...items: (Fn<T1> | Fn<T1>[] | ReadonlyArray<Fn<T1>>)[]): Fn<T1>[]; }
+>a : Fn<T>[]
+}
+

tests/baselines/reference/arrayConcatMap.types

@@ -4,9 +4,9 @@ var x = [].concat([{ a: 1 }], [{ a: 2 }])
 >[].concat([{ a: 1 }], [{ a: 2 }])          .map(b => b.a) : any[]
 >[].concat([{ a: 1 }], [{ a: 2 }])          .map : <U>(callbackfn: (value: any, index: number, array: any[]) => U, thisArg?: any) => U[]
 >[].concat([{ a: 1 }], [{ a: 2 }]) : any[]
->[].concat : { (...items: ReadonlyArray<any>[]): any[]; (...items: any[]): any[]; }
+>[].concat : { (...items: (any[] | ReadonlyArray<any>)[]): any[]; (...items: any[]): any[]; }
 >[] : undefined[]
->concat : { (...items: ReadonlyArray<any>[]): any[]; (...items: any[]): any[]; }
+>concat : { (...items: (any[] | ReadonlyArray<any>)[]): any[]; (...items: any[]): any[]; }
 >[{ a: 1 }] : { a: number; }[]
 >{ a: 1 } : { a: number; }
 >a : number

tests/cases/compiler/arrayConcat3.ts

@@ -0,0 +1,5 @@
+// TODO: remove lib hack when https://github.com/Microsoft/TypeScript/issues/20454 is fixed
+type Fn<T extends object> = <U extends T>(subj: U) => U
+function doStuff<T extends object, T1 extends T>(a: Array<Fn<T>>, b: Array<Fn<T1>>) {
+    b.concat(a);
+}